Experimental cookery

Piatt and Fleming have stained fats and oils with Sudan HI, a red dye soluble in fats but not soluble in water, and examined the baked products and the batter, in this case cookies, under the microscope. They find the fat to be in thin layers between the starch granules when the material is mounted dry. In some instances the fat completely surrounds the starch granules; in others the granules touch with no fat layer between them. These layers of fat, which physically separate different parts of the dough and prevent them from coming together in a solid mass, vary in thickness in different sections of the dough. To have the best shortening effect a fat must adhere to the flour particles and not be squeezed out by pressure. They give the following order for the shortening power of different fats, lard having the greatest shortening power. Lard Lard compound Cottonseed oil Butter Coconut oil Vaseline > Purified petroleum oils, as Nujol 568 FATS AND OILS For these differences In shortening power, Piatt and Fleming have sug- gested that the following factors have minor or major effect: viscosity, surface tension of oil, the melting point of the fat, and orientation of the molecule due to double bonds of the fatty acid chains of the glycerides. The following is a short summary of their article. Viscosity gives a fat the power of spreading easily in the dough ; a more viscous fat will run out of the dough less readily in baking, but it is of relatively little importance in shortening power, as shown by the fact that some of the petroleum products were as viscid as lard but gave less shorten- ing power. A melting point close to that of lard seems desirable, yet this factor alone is not a satisfactory explanation in all cases, as coconut oils may be prepared having the same melting point as butter but less shortening power. Plasticity gives a fat the ability to spread easily, which is beneficial ; but the fact that the oils having no plasticity give greater shortening power than butter shows that plasticity is only one of the important factors. Owing to orientation of molecules, fats containing unsaturated glycerides cover a greater surface area than those with saturated glycerides. The shortening power of fats tested, with the exception of lard and lard com- pound, was in the same order as the percentage of unsaturated glycerides contained by the fats. The author has found that an oil is partially or wholly emulsified as an oil-in-water emulsion in uncooked cake batter. However, the cake batter contained milk and egg, whereas the cooky batter of Piatt and Fleming did not contain milk. In cake batters an unmelted fat is distributed in sheets, layers, or films of different thicknesses between the starch granules, and around the air bubbles and sugar crystals. Whether the oil remains emulsified during baking of a cake batter might have some effect on the finished product, but the distribution of the oil or fat when the batter or dough is being mixed undoubtedly affects the tenderness, for this is the period w^hen the gluten is being developed.